WASHINGTON—The United States has so many bridges in need of repair or replacement, and so little money to do the work, that state and local officials say they are engaged in a kind of transportation triage: They fix the most important and vulnerable spans first, nurse along others and, when there’s no hope, order a shutdown.

Many of today’s aging bridges carry more vehicles than they were originally expected to handle; truckloads that pass over are much heavier, too. Many also are years past their designed life expectancy.

They are expensive to fix and far more costly to replace—sometimes billions of dollars for a single bridge.

Of special concern are bridges that are both “fracture critical” and “structurally deficient.” A bridge is deemed fracture critical when there’s no backup to protect against collapse if a single key element fails. Structurally deficient means it is in need of rehabilitation or replacement because at least one major component has advanced deterioration or other problems that lead inspectors to deem its condition poor or worse.

An Associated Press analysis of 607,380 bridges in the most recent federal National Bridge Inventory showed that 65,605 were classified as structurally deficient and 20,808 as fracture critical. Of those, 7,795 had both red flags.

“Those would be ones you’d worry about more,” said Ted Zoli, chief bridge engineer for HNTB Corp. in New York.

Officials say the bridges are safe. And despite the ominous-sounding classifications, engineers say that even bridges that are structurally deficient and fracture critical should not collapse if monitored and maintained properly.

“We have a term for unsafe bridges, and that is ‘closed,’ ” said Massachusetts State Highway Administrator Frank DePaola.

The AP focused on the bridges that fit both criteria. Together, they carry more than 29 million drivers a day, and many were built more than 60 years ago. Located in all 50 states, as well as Puerto Rico and the District of Columbia, they serve communities of all sizes, and include crossings on low-travel rural roads and busy spans like the Brooklyn Bridge in New York, the Main Avenue Bridge in Cleveland and the Frederick Douglass Memorial Bridge in the nation’s capital.

Finding the money to finance repairs or replacement remains a critical issue.

After the collapse six years ago of the Interstate-35W bridge in Minneapolis, state lawmakers raised the Minnesota gas tax to finance a 10-year construction program for the most serious problem bridges. Some $1.2 billion has gone into the effort so far, according to the state Department of Transportation. The campaign has helped to cut the state’s original list of 172 problem bridges roughly in half.

In Maine, the I-35W collapse also prompted the state Legislature to approve extra funding of $40 million a year over four years. Maria Fuentes of the Maine Better Transportation Association said the state is plagued by older bridges and funding shortfalls, which are greater now that the supplemental funding program has ended.

“We do well with the money that we have, but we’re getting to the point where if there isn’t an influx of money, we’re kind of rolling the dice,” she said.

Mike Vehle, a Republican state senator in South Dakota, said everyone “wants good roads and bridges. No one wants to pay for it.”

“We have a funding problem,” agreed Dennis Heckman, the state bridge engineer for the Missouri Department of Transportation. Still, he said, motorists “should not be afraid to drive across the bridge.”

His words echoed assurances given by state transportation officials across the country: Careful inspections are conducted regularly, they said, and when warranted, the frequency of checkups is increased. Also, when necessary, weight limits are placed on bridges.

The number of bridges nationwide that are both structurally deficient and fracture critical has been fairly constant for a number of years, experts say. But both lists fluctuate frequently, especially at the state level, since repairs can move a bridge out of the deficient categories while spans that become more dilapidated can be added. There also is considerable lag time between when state transportation officials report data to the federal government and when updates are made to the National Bridge Inventory.

Finding money to replace structurally deficient and fracture critical bridges in rural areas is especially difficult. Light traffic tends to make those bridges a low priority even though they may be keenly important to people in the region.

In Brown County on the northern border of South Dakota, for example, four bridges fall into both safety categories, each of them a century or more old. One has already been closed. The other three are dying of old age, said county highway superintendent Jan Weismantel, but they should be safe as long as drivers don’t exceed restrictions placed on the size of trucks and other vehicles—3 tons for one bridge, 5 tons for the other two. Those restrictions effectively limit bridge traffic to a car or light pickup truck.

All bets are off if someone drives a heavy truck or farm machinery across such a bridge, she said.

“Who’s to say that somebody’s not taking something that weighs more than 6,000 pounds across a 3-ton max bridge?” Weismantel said. “It’s kind of a gamble. It’s also very dangerous. Somebody could get killed.”

James White, a 33-year-old independent trucker, said he worries about the condition of some of the bridges he drives his 18-wheeler across in the mountainous terrain of eastern Tennessee.

“There are some that I go across with a 90,000-pound load, and I’m thinking, ‘If this bridge don’t hold me, I’m gone,'” he said while refueling at a truck stop in East Nashville.

Michigan bridges in both categories include some that don’t see much traffic. Three are over the Whitefish River in Alger County in the Upper Peninsula. They are steel truss bridges, with a surface made from timbers, and probably need to be replaced.

“I applied for federal bridge funds for five consecutive years. Each year I’m denied,” said Bob Lindbeck, engineer and manager of the Alger County Road Commission.

He said the condition of the bridges forces him to post weight restrictions, which in turn discourage people from living in the area year-round because snow plows and emergency vehicles can’t cross the bridges.

In eastern Kansas, Miami County engineer J.R. McMahon said many of his county’s bridges were built nearly a century ago, when farm equipment wasn’t much bigger than a modern full-size sport utility vehicle. As the bridges get older, they become “functionally obsolete” because they are too narrow to handle agricultural traffic, he said.

“It’s an issue of priority for the counties,” said Norman Bowers, local road engineer for the Kansas Association of Counties. “Do you spend money to replace a bridge when only 10 people a day use it?”

Pennsylvania has whittled down its backlog of structurally deficient bridges but still has many more to go. Some are among the busiest in the state, including the 85-year-old Liberty Bridge, spanning the Monongahela River from downtown Pittsburgh to its south side, and an I-95 span in Philadelphia’s lower northeast section along the Delaware River. And an estimated 300 bridges are in position to move onto the state’s structurally deficient list every year if no maintenance is done.

Many Pennsylvania lawmakers have long sought to boost transportation funding, in part to address crumbling bridges. But this year’s proposals, including Gov. Tom Corbett’s $1.8 billion plan, stalled amid fights over details.

New construction techniques are being employed in some states to significantly reduce the time it takes to replace deficient bridges. In some cases, most of the superstructure is being constructed off-site and then moved into place when piers and abutments are ready. States are also packaging bridge design and construction into a single contract, saving more time.

Massachusetts’ “Fast 14” project replaced 14 bridges on Route 93 near Boston in 10 weekends. State officials estimated the work would normally take at least four years, but the time was dramatically reduced by relying heavily on prefabricated parts.

Congressional interest in fixing bridges rose after the I-35W collapse in Minneapolis, but efforts to add billions of federal dollars specifically for repair and replacement of deteriorating bridges foundered. A sweeping transportation law enacted last year eliminated a dedicated bridge fund that had been around for more than three decades. State transportation officials had complained the fund’s requirements were too restrictive. Now, bridge repairs or replacements must compete with other types of highway projects for federal aid.

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